Device with a Waveguide with a Support Structure Comprising a Polymer Layer and Method for its Fabrication

Abstract

In an embodiment a device includes a device layer, a substrate defining a substrate plane extending through a point of the substrate being closest to the device layer, a waveguide configured to guide an electromagnetic wave, wherein the waveguide extends in a length direction in the device layer, and wherein the waveguide has a width in a device layer plane in a direction perpendicular to the length direction and a height out of the device layer plane in the direction perpendicular to the length direction and a support structure, wherein the support structure extends from the substrate to the device layer to support the waveguide on the substrate.

Claims

1.-36. (canceled)

37. A device comprising: a device layer; a substrate defining a substrate plane extending through a point of the substrate being closest to the device layer; a waveguide configured to guide an electromagnetic wave, wherein the waveguide extends in a length direction in the device layer, and wherein the waveguide has a width in a device layer plane in a direction perpendicular to the length direction and a height out of the device layer plane in the direction perpendicular to the length direction; and a support structure, wherein the support structure extends from the substrate to the device layer to support the waveguide on the substrate, wherein the device layer plane extends parallel to the substrate plane through the point of the device layer being supported via the support structure that is closest to the substrate plane, wherein the device layer is of a different material than a polymer, wherein the support structure comprises a polymer layer, wherein a comparison cross section extends parallel to the substrate plane through the polymer layer at a spacing perpendicularly from the substrate plane and extends perpendicularly to the length direction to a breadth, equal to the width of the waveguide, from a side of the support structure being closest to the waveguide, wherein the spacing is chosen to maximize a ratio of an area of the polymer layer within the comparison cross section to an area of the support structure within the comparison cross section, and wherein the ratio is at least 0.5.

38. The device according to claim 37, wherein the device layer is essentially parallel to the substrate plane.

39. The device according to claim 37, wherein the polymer layer is in contact with the device layer.

40. The device according to claim 37, wherein the device layer comprises a substructure, comprising at least one subelement, arranged at a distance from the waveguide, wherein the waveguide is connected to the substructure with a connector in the device layer, and wherein the support structure extends from the substrate to the substructure.

41. The device according to claim 40, wherein the substructure comprises a plurality of subelements.

42. The device according to claim 40, wherein the support structure comprises a plurality of support elements extending from the substrate to the substructure.

43. The device according to claim 40, wherein the connector comprises a plurality of bridges connecting the waveguide with the substructure.

44. The device according to claim 37, wherein the support structure extends from the substrate to the waveguide.

45. The device according to claim 44, wherein a width of the support structure at a point of support of the waveguide is smaller than the width of the waveguide.

46. The device according to claim 44, wherein the support structure comprises a plurality of support elements such that the waveguide is free-hanging between two adjacent support elements.

47. The device according to claim 46, wherein at least one of the support elements is made entirely of a polymer.

48. The device according to claim 37, wherein the waveguide comprises at least sections, separated in the length direction of the waveguide, and wherein the sections are free from contact with any material on a surface facing the substrate.

49. A method for fabricating a device comprising a device layer, a substrate defining a substrate plane extending through a point of the substrate being closest to the device layer, a waveguide for guiding an electromagnetic wave, wherein the waveguide extends in a length direction in the device layer, wherein the waveguide has a width in a device layer plane in a direction perpendicular to the length direction and a height out of the device layer plane in the direction perpendicular to the length direction, and a support structure, wherein the support structure extends from the substrate to the device layer to support the waveguide on the substrate, and wherein the device layer plane extends parallel to the substrate plane through a point of the device layer being supported via the support structure that is closest to the substrate plane, the method comprising: providing a handling substrate on which a device layer is arranged, the handling substrate and the device layer forming a device layer assembly; providing the substrate; providing a polymer contact layer on the substrate and/or on the device layer assembly on the same side of the handling substrate as the device layer; attaching the device layer assembly to the substrate with the device layer arranged between the handling substrate and the substrate so that the polymer contact layer forms a polymer layer; removing the handling substrate after attaching the device layer assembly to the substrate; removing a material from the device layer to form the waveguide; and removing a material from the polymer contact layer to form the support structure, wherein the device layer is of a different material than a polymer, wherein the support structure comprises the polymer layer, wherein a comparison cross section extends, parallel to the substrate plane through the polymer layer at a spacing perpendicularly from the substrate plane, and extends perpendicularly to the length direction to a breadth, equal to the width of the waveguide, from a side of the support structure being closest to the waveguide, wherein the spacing is chosen to maximize a ratio of an area of the polymer layer within the comparison cross section to an area of the support structure within the comparison cross section, and wherein the ratio is at least 0.5.

50. The method according to claim 49, wherein forming the waveguide is performed after removing the handling substrate.

51. The method according to claim 49, wherein forming the support structure is performed after removing the handling substrate.

52. The method according to claim 49, wherein a thickness of the polymer layer is formed to be in an interval of 5 nm to 100 μm inclusive.

53. The method according to claim 49, further comprising: forming, in the device layer, a substructure comprising at least one subelement arranged at a distance from the waveguide; and forming, in the device layer, a connector with which the waveguide is connected to the substructure, wherein the support structure is formed to extend from the substrate to the substructure.

54. The method according to claim 49, wherein the support structure is formed to extend from the substrate to the waveguide.

55. The method according to claim 49, further comprising forming metal lines and/or active devices in or on the device.

56. The method according to claim 49, further comprising removing a material from the substrate below the waveguide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The features described in relation to the second aspect are combinable with the method according to the fourth aspect.

[0081] In the following description of preferred embodiments reference will be to the appended figures on which:

[0082] FIG. 1 shows in a top view a device comprising a waveguide supported on a substrate according to an embodiment;

[0083] FIG. 2 shows in a perspective sectional view a part of the device in FIG. 2 according to an embodiment;

[0084] FIG. 3 shows the cross-section A-A in FIG. 2 according to an embodiment;

[0085] FIG. 4 shows the cross-section A-A in FIG. 2 according to another embodiment;

[0086] FIG. 5a shows in a top view a part of a device according to an alternative embodiment;

[0087] FIG. 5b shows in a top view a part of a device according to an alternative embodiment;

[0088] FIG. 6 shows the cross-section B-B in FIGS. 5a and 5b;

[0089] FIG. 7 shows the cross-section C-C in FIGS. 5a and 5b according to two different embodiments;

[0090] FIG. 8 shows a cross-section of a part of a device according to two different embodiments; and

[0091] FIGS. 9a-9f illustrate the method for fabricating a device according to FIGS. 1-8.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0092] In the following description of embodiments of the invention the same reference numerals will be used for equivalent features in the different figures. The figures are not drawn to scale.

[0093] FIG. 1 shows in a top view a device 1 according to an embodiment. The device comprises a waveguide supported by support elements 8 on a substrate 2. The waveguide defines a closed circuit along a length direction L. FIG. 2 shows in a perspective sectional view a part of the device in FIG. 2 according to an embodiment.

[0094] FIG. 3 shows the cross-section A-A in FIG. 2 according to an embodiment. The device will initially be described with reference to primarily FIGS. 2 and 3. The device 1 (FIG. 1) comprises, a device layer 4, a substrate 2 defining a substrate plane 3 extending through the point of the substrate 2 being closest to the device layer 4, and a waveguide 7 for guiding an electromagnetic wave. The side of the device layer 4 facing the substrate 2 defines a device layer plane 5 (FIG. 3). The waveguide extends in a length direction L (FIGS. 1 and 2) in the device layer 4. The waveguide 7 has a width w in the device layer plane 5 (FIG. 3) in a direction perpendicular to the length direction L, and a height h out of the device layer plane 5 (FIG. 3) in a direction perpendicular to the length direction L. The waveguide 7 is supported on the substrate 2 via a support structure 6 extending from the substrate 2 to the device layer 4. A device layer plane 5 extends parallel to the substrate plane 3 through the point of the device layer 4 being supported via the support structure 6 that is closest to the substrate plane. In the figures the device layer is perfectly flat resulting in the device layer plane 5 coinciding with the side of the device layer 4 facing the substrate 2. In the embodiment of FIGS. 1-3 the side of the waveguide 7 facing the substrate 2 is partly free from contact with the support structure, which is clearly visible in FIG. 2 wherein the support element 8, which forms part of the support structure 6, only extends along a limited length of the waveguide 7. The waveguide is free-hanging on both sides of the support element 8 in FIG. 2. Thus, the waveguide 7 comprises sections 80, separated in the length direction of the waveguide 7, which sections 80 are free from contact with any material on the surface facing the substrate 2.

[0095] The width w and height h of the waveguide determines a maximum wavelength that is suitable to transmit by the waveguide. The distance, perpendicular to the substrate plane 3, between the device layer plane 5 and the substrate plane 3, is denoted D2 in FIG. 3. The maximum distance, perpendicular to the substrate plane 3, consisting of free-space between the waveguide 7 and any solid material below the waveguide is denoted D1 in FIG. 3. In the embodiment shown in FIG. 3 D2 is equal to Dl. The device layer 7 is of a different material than a polymer, and the support structure 6 comprises a polymer layer 18. In FIGS. 2 and 3 the polymer layer 18 extends from the substrate 2 to the device layer 4 and is also in contact with the substrate 2 and the device layer 4. Thus, the support element 8 is made entirely of polymer. The device layer plane 5 is parallel to the substrate plane 3. Shown in FIG. 2 is a comparison cross section 25 which is parallel to the substrate plane 3, extends through the polymer layer 18 at a spacing y perpendicularly from the substrate plane 3, and extends perpendicularly to the length direction L to a breadth x, equal to the width w of the waveguide, from a side s of the support structure 6 being closest to the waveguide. The spacing y is chosen to maximize a ratio r of the area of the polymer layer within the comparison cross section 25 to the area of the support structure within the comparison cross

section 25. In this case the support structure is made entirely of a polymer and the ratio is 1 irrespective of the spacing y. The comparison cross section 25 extends along the entire length of the waveguide.

[0096] The device 1 shown in FIGS. 1-3 alleviates the problems with mechanical stresses in device layer 4 and the waveguide 7 irrespective of the distance D2 perpendicular to the substrate plane 3, between the device layer plane 5 and the substrate plane 3. The distance D2 can be made larger than 10 μm without introducing mechanical stresses in the device layer.

[0097] However, in order to alleviate also the problems with losses from the waveguide the maximum distance Dl, perpendicular to the substrate plane 3, consisting of free-space between the waveguide 7 and any solid material below the waveguide 7, should be at least 2 μm.

[0098] Another big advantage with having a polymer layer is that the device layer can be made thin. The ratio of the largest distance D1, perpendicular to the substrate plane 3, between a free surface of the waveguide 7 facing the substrate and any solid material to the height h of the waveguide 7 may be more than 6, i.e. Dl/h>6. Preferably Dl/h>8, and most preferred Dl/h>10. By having Dl/h>6, the losses due to leakage of energy from the waveguide to the substrate are very low for wavelengths suitable for the height. Also, the ratio of the distance D2, perpendicular to the substrate plane 3, between the device layer plane 5 and the substrate plane 3 to the height h of the waveguide 7 is more than 6, i.e. D2/h>6, preferably D2/h>8, and most preferred D2/h>10.

[0099] With a structure according to the embodiments in FIG. 2 and FIG. 3 the distance between the substrate 2 and the device layer 4 may be made considerably thicker than has been done in the prior art with almost no mechanical stresses in the device layer. Also, the losses from the waveguide are alleviated in comparison to the prior art due to the favorable properties of polymer with regard to affecting the electromagnetic wave in the adjacent waveguide 7. Also, in absolute quantities the distance D2, perpendicular to the device layer plane 5, between the device layer plane 5 and the substrate plane 3 can easily be manufactured to be bigger than 2 μm, preferably 3 μm, more preferably 30.1 μm, more preferably 4 μm, more preferably 6 μm, and most preferred 10 μm. Alternatively, it is of course possible to make the polymer layer thin. The polymer layer may be as thin as 5 nm.

[0100] The width ws of the support structure 6 at the point of support of the waveguide 7 is smaller than the width w of the waveguide 7 as can be seen in FIG. 3. It is possible to have the width ws of the support structure 6 at the point of support of the waveguide 7 larger than the width w of the waveguide 7.

[0101] FIG. 4 shows the cross-section A-A in FIG. 2 according to another embodiment. In contrast to the embodiment of FIG. 3 the device shown in FIG. 4 comprises more layers. More specifically 5 layers are shown in FIG. 4. The substrate 2 may be a silicon substrate and the device layer 4 and waveguide 7 may be of silicon. The layer 13 in contact with the substrate 2 may be a thick oxide layer. As is indicated by the parts of the thick oxide layer 13 on the sides the thick oxide layer may have covered the entire substrate before commencing fabrication of the device. The layer in contact with the waveguide 7 may be a metal layer 14. The metal layer 14 may be used during fabrication of the device. Finally, the layer between the thick oxide layer 13 and the metal layer 14 may be a polymer layer 18, which constitutes the contact layer 22, 23. The polymer layer 18 functions as a mechanical contact layer during fabrication of the device as will be evident from the description of the method below. Also, in this case, the ratio r is 1 as the polymer layer 18 extends from side to side of the support element 8.

[0102] The materials in the substrate 2, the support structure 6 and the device layer 4/waveguide 7, may be chosen from the materials indicated below. However, as is indicated by the different hatchings the material of the support structure 6 in contact with the device layer 4 is different from the material in the device layer, and the material of the support structure 6 in contact with the substrate 2 is different from the material in the substrate. Also, D1 and D2 are equal to each other in FIG. 4.

[0103] In the embodiments shown in FIGS. 2-4 the device layer 4 is equivalent to the waveguide 7. However, the term device layer more generally refers to the layer from which the waveguide is fabricated. Another common feature is that the device layer plane 5 is essentially parallel to the substrate plane 3.

[0104] FIG. 5a shows in a top view a part of a device according to an alternative embodiment. In FIG. 5a the device layer 4 comprises a substructure 11, comprising a plurality of subelements 12 arranged at a distance from the waveguide 7, wherein the waveguide 7 is connected to the substructure 11 with connection means 15 in the device layer 4 in the form of a plurality of bridges 16. The support structure 6 is in the form of a plurality of support elements 8 which each extend from the substrate 2 to a respective subelement 12. The substructure 11 is connected to the waveguide 7 with a plurality of bridges 16, which each extend from the waveguide to a respective subelement 12. The support elements 8 comprise a polymer. The distance between the support structure 6 and the waveguide 7 is denoted D3 in FIGS. 5a and 5b. The ratio of said distance D3 to the width w of the waveguide 7 is about 2-3 in FIG. 5 but may be as big as 100 and as small as 1. FIG. 5b shows in a top view a part of a device according to an alternative embodiment. In FIG. 5b the connection means 15 are in the form of a continuous membrane 24. Due to the fabrication process of a membrane, the membrane 24 might contain holes (not shown) which are necessary if material needs to be removed underneath by under etching. The membrane 24 extends along each side of the waveguide 7 as is shown in FIG. 5b. The comparison cross section 25 extends between the two parallel lines 30, 30′ in FIG. 5a. The distance between the two lines 30, 30′, corresponds to the extension x of the comparison cross section 25. The extension x is equal to the width w of the waveguide. In FIGS. 5a and 5b two of the support elements comprises core elements 33 made of a conductive material. This will lead to a ratio r being less than 1. As the comparison cross section extends along the entire length of the waveguide it is not possible to determine the ratio r from FIGS. 5a and 5b. However, assuming that the pattern shown in FIGS. 5a and 5b repeats itself along the entire length of the waveguide, i.e., that every second pair of support elements comprise a core element 33 made of a conductive material, the ratio r is more than 0.95 in the embodiment shown in FIGS. 5a and 5b.

[0105] FIG. 6 shows the cross-section B-B in FIGS. 5a and 5b which both have the same cross sections. From FIG. 6 it is evident that the height hb, hm, of the bridges 16 and the membrane 24, respectively, is a smaller than the height h of the waveguide 7. This difference in height between the waveguide 7 and the connection means 15 will ensure proper confinement of the electromagnetic wave within the waveguide 7. It is also shown in FIG. 6 that material has been removed from the substrate 2 below the waveguide 7 resulting in that the maximum distance D1, perpendicular to the substrate plane 3, consisting of free-space between the waveguide 7 and any solid material below the waveguide is larger than the distance D2, perpendicular to the substrate plane 3, between the device layer plane 5 and the substrate plane 3. Thus, Dl>D2 in the embodiment shown in FIG. 6. The materials of the different layer can be chosen as described below. The height of the connection means in FIG. 6 is less than 80% of the height h of the device layer.

[0106] FIG. 7 shows the cross-section C-C of FIGS. 5a and b according to two different embodiments. In the embodiment to the left in FIG. 7 the support element 8 is made of metal and extends from the substrate through the device layer. In the embodiment to the right in FIG. 7 the support element 8 comprises a core element 33 made of a conductive material and extends from the substrate 2 through the device layer 4. The support element is also surrounded by a different material. When fabricating a support element as shown to the right the structure shown in FIG. 6 is first fabricated. A hole is then formed through the device layer and the support element 8.

[0107] Finally, the hole is filled with metal to arrive at the structure shown to the right in FIG. 7. In order to arrive at the support element shown to the left in FIG. 7 the material surrounding the core element 33 is removed. A metal connection between the substrate 2 and the device layer

is useful to provide an electrical connection between a device in the substrate 2 and a device in the device in the device layer 4.

[0108] FIG. 8 shows a cross-section of a part of a device according to two different embodiments. The embodiments shown in FIG. 8 both comprise a substrate 2 on/in which metal lines 19 and different active devices 20 have been formed such as FETs (Field Effect Transistors). The metal lines 19 and the active devices 20 are embedded into an oxide layer.

[0109] The support elements 8 on top of the oxide layer 21 forms part of the support structure 6. The oxide layer 21 also forms part of the support structure 6. The oxide layer 21 and the support elements 8 together forms the support structure 6.

[0110] The comparison cross section 25 is indicated in FIGS. 2, 4, 6, 7, and 8, by its extension x perpendicularly to the length direction from a side of the support structure 6. The extension x is equal to the width w of the waveguide 7. The distance D3 between the waveguide 7 and the support elements 8 is slightly larger than the width w of the waveguide 7 in the embodiments shown in FIGS. 6-8.

[0111] In all embodiments described above it is advantageous to have the width w of the waveguide 7 at least 5 times the height h of the waveguide 7. By designing the waveguide in this way, the electromagnetic wave in the waveguide will be affected primarily by the top and bottom sides of the waveguide and to a smaller extent by the sides between the top and bottom sides. As it is easier to control the quality of the top and bottom sides said ratio will ensure a good quality of the waveguide.

[0112] In all embodiments described above the height h of the waveguide 7 is preferably smaller than the wavelength of the electromagnetic wave to be guided in order to better control the mode of the electromagnetic wave through the waveguide 7.

[0113] The embodiments are aimed at providing a device as defined in the claims, wherein the waveguide 7 is optimized for guiding an electromagnetic wave with a wavelength within the range of 0.4-100 μm, preferably 1.2-20 μm, and most preferred within 3-12 μm.

[0114] The devices described above may comprise metal lines 19 (FIG. 1) and/or active devices 20 (FIG. 1), such as transistors, light sources and detectors, in or in contact with the device layer 4 and/or the substrate 2.

[0115] FIG. 9a-9f illustrates a method for fabricating a device according to FIG. 3 according to an embodiment. The method starts with the provision of a handling substrate 26 on which a device layer 4 is arranged. In the example shown in FIG. 9a the handling substrate 26 is a silicon wafer which has been oxidized to produce an optional intermediate layer 28 in the form of a Si02-layer. A device layer 4 has then been fabricated on the intermediate layer 28. The handling substrate 26, the intermediate layer 28 and the device layer 4 form a device layer assembly 27. Also, a substrate 2 is provided on which a contact layer 22 is provided. As an alternative to the embodiment shown in FIG. 9 it is possible to provide a contact layer 23 on the handling substrate 26, in addition to or instead of the contact layer 22 on the substrate 2. This optional contact layer 23 is shown with dashed lines in FIG. 9a. As an example, the contact layer(s) 22, 23, may be polymer layers or oxide layers. Preferably, the contact layers 22, 23 may be polymer layers. Below is a list of possible polymers that may be chosen for the contact layer.

[0116] In a second step illustrated in FIG. 9b the device layer assembly 27 is attached on the substrate 2 with the device layer 4 arranged between the handling substrate 26 and the substrate 2, using the contact layer(s) as a connecting layer. The attachment of the device layer assembly 27 to the substrate 2 is performed by applying, e.g., a pressure and heat to the handling substrate 26 and the substrate 2. The application of heat and pressure should be interpreted broadly. A temperature as low as 20° C. and a pressure as low as 0.1 bar may be sufficient. Depending on the material used in the contact layer(s) 22, 23, the temperature and pressure applied may vary. When using polymer as contact layer(s) 22, 23, a suitable temperature interval is 20-500° C. Preferably, a temperature between 20-250° C. is used. A suitable pressure at the bond interface applied between 0.1-200 bar. When polymer is used as contact layer(s) 22, 23, the bonding can be performed in vacuum or atmospheric pressure. A polymer layer is advantageous as contact layer as the use of polymer might decrease losses in the waveguide due to reduced absorption. Further, the use of polymer enables wafer bonding at low temperatures which allows the use of substrates with low thermal budget, e.g., due to preprocessing or material properties. Also, polymer bonding allows joining of components of various material, which enables the use of these materials as waveguide, support structure and substrate. Certain combinations reduce the losses in the device and/or might reduce fabrication cost of the devices. That is partly due to the fact that a multitude of polymers can be applied in liquid/semi-liquid form using spin coating, which is a very easy and cheap process.

[0117] When using oxide as contact layer(s) 22, 23, the temperature used during bonding should be kept below 1200° C. Depending on the bonding method, a temperature between 15-400° C. or even 15-200° C. is used. The effective pressure at the bond interface applied during bonding can be zero or up to 200 Bar. Even if an oxide layer is not quite as easy to form as a polymer layer, an oxide layer is still quite easy to form. A benefit of having an oxide as the contact layer is that is more heat resistant than polymer. The higher heat resistance gives more freedom when choosing processing methods after formation of the contact layer.

[0118] Alternatively, the contact layer(s) 22, 23, may be formed as a metal layer. It is easy to form a metal layer, a metal layer is more heat resistant than a polymer layer, has more long-term stability than polymer and require lower bonding temperature than oxide bonding. Suitable metals for the contact layer are Copper, Gold and Aluminium. When using one of said metals as contact layer(s) 22, 23, the temperature used during bonding is preferably 20-450° C. A suitable pressure is 0.1-200 bar.

[0119] In a third step illustrated in FIG. 9c the handling substrate 26 and the optional intermediate layer 28 are removed after attachment of the device layer assembly 27 to the substrate 2.

[0120] Preferably, a suitable etching technique is used to remove the handling. The etching technique is chosen according to the material in the handling substrate 26.

[0121] In a fourth step illustrated by FIG. 9d material is removed from the device layer 4 to form the waveguide 7. The material in the device layer 4 is preferably removed using an etching technique adapted to the material in the device layer 4. As an alternative it is possible to form the waveguide 7 before the step of attaching the device layer assembly on the substrate 2.

[0122] In a fifth step illustrated by FIG. 9e and a sixth step illustrated by FIG. 9f material is removed

between the device layer and the substrate to form the support structure 6 as has been described above, so that the side of the waveguide 7 facing the substrate 2 is at least partly free from contact with any solid material, so that the ratio of the largest distance Dl, perpendicular to the substrate plane 3, between a free surface of the waveguide 7 facing the substrate and any solid material to the height h of the waveguide 7 is more than 6, i.e. Dl/h>6, preferably Dl/h>8, and most preferred Dl/h>10, and so that the ratio of the distance D2, perpendicular to the substrate plane 3, between the device layer plane 5 and the substrate plane 3 to the height h of the waveguide 7 is more than 6, i.e. D2/h>6, preferably D2/h>8, and most preferred D2/h>10. The material between the device layer 4 and the substrate 2 is preferably removed in a two-step process. In a first removal step illustrated by FIG. 9e the material in the contact layer(s) 22, 23, is removed on the sides of the waveguide by a vertical etching method. In a second removal step illustrated by FIG. 9f material is removed below the waveguide 7 using under-etching in order to form the support structure 6. The support structure 6 is formed to extend from the substrate 2 to the waveguide 7.

[0123] As an alternative the forming of the support structure may be performed before the step of removing the handling substrate. According to this alternative the support structure is preferably formed before attachment of the device layer assembly 27 on the substrate 2.

[0124] The method may also comprise the steps of forming, in the device layer 4, a substructure 11 arranged at a distance from the waveguide 7, and forming, in the device layer 4, connection means 15 with which the waveguide 7 is connected to the substructure 11. The support structure 6 is formed to extend from the substrate 2 to the substructure 11. In order to arrive at the device according to FIGS. 5a and 6 the substructure 11 is formed as a plurality of subelements 12, and the connection means 15 is formed as a plurality of bridges 16.

[0125] In order to arrive at the device according shown to the right in FIG. 7 the method comprises the steps of removing material in regions between the substructure 4 and the substrate 2 and forming a core element 33 in each one of said regions. The core elements 33 may comprise a conductive material. In order to arrive at the device shown to the left in FIG. 7 the material surrounding the core element 33 is removed to arrive at a support element 8 being constituted by the core element 33.

[0126] The thickness chosen for the contact layer(s) 22, 23, depends on many different parameters. Preferably, the thickness of the contact layer is in the interval 5 nm to 100 μm. The low part of the interval requires the support structure 6 to be constituted by other materials apart from the contact layer(s) 22, 23, as is shown in FIG. 4. A useful choice of material for the contact layer is a polymer. A thickness in the interval 5 nm-100 μm, constitutes the extremes of what is possible with adhesive bonding e.g. by using a bonding polymer. However, in order to provide a reliable contact layer(s) 22, 23, the thickness of the polymer contact layer(s) is preferably 200 nm-50 μm, most preferably 3-20 μm. A thickness in the interval 200 nm-so urn are the commonly used thicknesses for adhesive bonding with a polymer. With a thickness in the interval 3-20 urn the support structure might consist entirely of polymer and the separation between waveguide and substrate allows the application in gas sensing. If a polymer thicker than 100 μm is used, the mechanical stability of the device might become critical.

[0127] As is shown in FIG. 8 the method may comprise the step of forming metal lines 19 and/or active devices 20, such as transistors, light sources and detectors, in or in contact with the substrate 2 and/or the device layer 4 and/or between the device layer 4 and the substrate 2.

[0128] Lists of Materials for the Different Layers

[0129] In the following lists of suitable materials for the different layers will be displayed.

[0130] The material in the waveguide 7, i.e., device layer 4, may be chosen from the following materials:

[0131] silicon, silicon germanium, germanium, silicon nitride, lll-V materials, such as GaAs, InP, InGaAs, and InGaP, chalcogenide glass, indium(l11)-fluorid, diamond, sapphire, lithium niobate and other nonlinear materials, piezoelectric materials.

[0132] The material in the substrate 2 may be chosen from the following materials:

[0133] silicon, CMOS, glass (Si02-based glasses), germanium, polymer sapphire, III-V materials, such as GaAs, InP, InGaAs, InGaP, etc., diamond, metals, silicon carbide

[0134] The material between the substrate and the device layer might be a combination of different materials stacked horizontally or vertically. These different materials may be chosen from the following materials:

[0135] polymer, metals (TiW, Ni, Au, W, Al, Cr, Ti, Cu, Ag), dielectrics (Si02, SiN, Al203), semiconductors such as, e.g., Si, SiGe.

[0136] The polymer may be chosen from the following materials polymer adhesives, thermoplastic polymers, thermoset polymers, elastomers, hybrid polymers, specific polymer adhesives such as, e.g., BCB, nanoimprint resist, epoxy, SU8, PDMS, and PMMA.

[0137] The invention is not limited to the described embodiments but may be amended in many ways without departing from the scope of the invention, which is limited only by the appended claims.